A senior Metropolitan police officer directly involved in the shooting of Jean Charles de Menezes, the Brazilian mistaken for a terrorist, has revealed he was not aware of the error until the following day. The detailed account given by Deputy Assistant Commissioner Alan Given, who retired last week, lends public support to the contested version of events provided by the force's embattled commissioner, Sir Ian Blair.

Mr Given was the most senior officer directly responsible for the CO19 firearms team that killed Mr de Menezes at Stockwell tube station on July 22 last year, the day after a series of attempted bombings brought chaos to tubes and trains across the capital. "When I left [the office at 11pm that Friday] I had no indication the wrong person had been shot," he told the Observer newspaper yesterday. "[Assistant Commissioner Alan Brown] had no clue that we had made a mistake. I did not learn the truth until the following day." His office, Mr Given said, was next door to Sir Ian's private office. "All I can say is that if they told him, they didn't tell me."

There were fresh claims last week that Sir Ian's office had been alerted to the mistake as early as the afternoon of July 22. The allegations followed calls for Sir Ian to resign after it was disclosed the commissioner had recorded private conversations with the attorney general, Lord Goldsmith.

Fears of further terrorist onslaughts had been fuelled by the discovery the previous evening of a fifth bomb abandoned at Wormwood Scrubs. The force felt the need to "do something, and fast", Mr Given said. There had initially been relief when news of the shooting broke since it was believed a suspect wanted for the July 21 attacks had been intercepted.

Later that day, Mr Given said, he spoke to the CO19 team responsible for the shooting at a police station in east London. "They were sombre, clearly concerned that they had shot a man dead. There wasn't even a sniff of the fact that there had been a tragic mistake. There was no rejoicing but the mood was buoyant," he said. "They were behaving in a very professional way. They had done the job that we ask firearms officers to do - to go out into potentially dangerous situations and shoot somebody."

He had also talked to the police commander who is understood to have given the order to carry out the shooting. He said she seemed "confident" she had done the right thing. The officers directly involved were also "convinced" they had killed somebody directly linked with the terrorist attacks of the day before. The former deputy assistant commissioner said he had been prompted to speak out because of the sustained attack on Sir Ian. "It feels unwarranted and unfair in its scale and lack of proportionality," he said.

Scotland Yard said yesterday the shooting was still under investigation by the Independent Police Complaints Commission. It added that Mr Given had been speaking in a private capacity.